The art of the present invention relates to sludge separation systems and methods in general and more particularly to an apparatus and method for continuously separating and deeply dehydrating suspended sludge solids in a liquid medium, especially lime (Ca(OH)2) particles and suspended manure sludge, as may be found in lagoons. The art of the present invention optimally benefits the environment, both during use, with a minimum of energy utilization, and via the separation of the solids which may be utilized or disposed of properly. The apparatus is usable in any liquid/suspended solid separation application, including but not limited to municipal wastewater treatment facilities, provided the specific gravity of the suspended solid is greater than that of the suspending liquid.
From time to time, lagoons, which are usually earthen pits used to collect waste, become filled with sludge. This sludge will usually range from 3% to 12% solids and the remainder is water. The aforesaid lagoons must be pumped from time to time to remove the solids and make room for future deposits. Conventional solid removal typically utilizes a pump to transfer the aforesaid thin slurry into tank trucks at 7,000 to 9,000 gals. per load and haul said slurry a considerable distance (average 15 miles in Iowa) for spreading on fields as fertilizer. Typically, the entity or operator performing said spreading is paid for the weight of solids removed from the lagoon and not the liquid or water in which said solids are suspended. The cost of hauling the aforesaid mix is approximately 78% of the combined costs of removal and spreading. From the aforesaid, it is apparent that a reduction of truck loads hauled by 70 to 80% would greatly increase profit margins for said entity. This profit margin increase is only realistic if the cost of removing the excess liquid or water is reasonable. Prior art attempts to dehydrate the aforesaid have failed to fully develop an apparatus or method that will perform the desired deep dehydration at a rapid and economical rate.
The present art apparatus and method provides the desirable cost effective dehydration in a compact, portable, effective, and energy efficient apparatus and method of use. The present art settling grid separator apparatus, when utilized with the method herein described, will perform sludge treatment or de-watering at an input rate of more than 1,000 gallons per minute (gpm) and deliver a substantially clear fluid or water discharge of approximately 800 gpm with a solids discharge of 70 to 80% solids to liquid or water ratio. The substantially clear liquid or water discharge can be returned to the lagoon of origination, thereby avoiding the need for transport. The aforesaid solid discharge is hauled to a storage or disposal site, used as fuel, or spread on fields as a fertilizer. With the present art, not only is the number of loads to be hauled greatly decreased but due to the deep dehydration, the utilization options are expanded for the solid portion of the former lagoon contents. Unique to the present art is the ability of the settling grid separator to perform the aforesaid separation in an energy conserving way, relying primarily upon gravitational separation, and this machine is a compact transportable apparatus.
Prior art attempts at sludge separation have been characterized by limited separation capability, short times between required maintenance, high energy utilization, environmentally degrading impact, and limited transportability. Prior art sludge separation devices such as that described by Hodges et al. in U.S. Pat. No. 6,652,757, entitled Method for High-speed Dewatering of Slurries, utilize tracking filter screen separation. The tracking filter screens are easily blocked with fine solid particles, thereby significantly decreasing the filtration rate, slowing slurry de-watering, and further requiring continual filter screen washing or replacement and disposal. The aforesaid art further requires significant energy input for belt pressing of the minimally de-watered slurry. Further prior art sludge separation devices as described by McGivern in U.S. Pat. No. 4,028,249, entitled Sewage Settling Tank, provide a series of submerged horizontal decks where solid particles deposit and a floating siphon system for removal of the deposited sludge slurry on the decks. This technique utilizes large amounts of energy for pumping the deposited slurry solid against gravitational forces, does not provide a deep dehydration, and is also not suitable for easy transport, quick setup, or large volume applications. Further prior art separation devices as described by Hodges et al. in U.S. Pat. No. 5,656,174, entitled Dredging System and Method, utilize inefficient energy consuming elements such as cyclones or centrifuges for secondary centrifugal separation.
The present art apparatus and method of use provides solid separation at up to an 80% solids to liquid ratio via utilization of a flocculating apparatus, gravitational settling apparatus, trap system, filter system, a controlled and even solid cake removal system, and a discharge conveyor system. The present art settling grid separator is a solids-liquid, gravity-separating machine, that is scaleable in size and capacity. The settling grid separator can be scaled up to operate at 20,000+gpm, which makes the settling grid separator an attractive system for river, harbor and lake dredging. Utilization of the unique design features provides very high settling rates with a minimum of energy expended. With the combination of water traps and pressure assisted vertical filters a deep dehydration of solids is achieved. The apparatus typically receives a 1,000 gallon per minute (gpm) sludge stream with 2 to 20% solids from a supply line fed with a dredge or other lagoon evacuation system. The system thereafter discharges 70% or greater solids and clear effluent. The apparatus is especially useful with sludge having a specific gravity of 1.25 or greater.
Typically the apparatus is mounted upon a trailer and transported to the sludge-pumping site, i.e. lagoon, and set up within an hour. That is, the trailer is positioned whereby the intake dredge pipe coupling, typically an 8″ cam-lock pipe coupling, faces the discharge pipe of the dredge. The trailer is leveled and an effluent hose is laid from the liquid discharge outlet of the apparatus back to the lagoon or wherever substantially clear discharge liquid or water is desired. When operated, removed solids with limited moisture content are discharged through a discharge chamber onto a conveyor and thereafter loaded into a truck for transport, thereby eliminating transport of the liquid redirected into the lagoon. Additional dehydration can be achieved by employing novel drying devices and adding them to the system between the discharge chamber and transport truck.
Accordingly, it is an object of the present invention to provide a settling grid separator apparatus and method of use which is capable of substantially separating suspended sludge solids in a liquid medium in an energy efficient manner.
Another object of the present invention is to provide a settling grid separator apparatus and method of use which provides the aforesaid solid separation in a transportable and scalable form.
Another object of the present invention is to provide a settling grid separator apparatus and method of use which economically provides deep dehydration of suspended solids at a rapid rate.
A further object of the present invention is to provide a settling grid separator apparatus and method of use which requires a minimum of maintenance or filter component replacement.
A further object of the present invention is to provide a settling grid separator apparatus and method of use which optimally introduces a flocculating agent into the input sludge stream based upon measured sludge flow and density measurements.
A still further object of the present invention is to provide a settling grid separator apparatus and method of use which provides solid separation utilizing primarily gravimetric, densimetric, and hydrometric techniques to separate suspended solids within a liquid carrier.
A yet further object of the present invention is to provide a settling grid separator apparatus and method of use which provides environmental benefits, both during use and as a product of use, heretofore not found in prior art sludge separation or treatment devices.